Method for producing cryogenic, solid monopropellants and solid propellants produced according to said method

ABSTRACT

The invention relates to a method for producing (cryogenic) solid monopropellants which are cooled to below room temperature and are used for rocket drives, especially using heterogeneous liquid-solid propellants wherein at least one of the reactants in the form of an oxidizer or a fuel contains a phase which is liquid or gaseous at normal temperature, for example emulsions of liquid constituents which do not dissolve in each other, suspensions of solid in liquid constituents or liquid-impregnated feed materials. The invention also relates to a cryogenic solid propellant for rocket drives, especially heterogeneous quasi-monopropellant fuel-oxidizer combinations. The aim of the invention is to increase the efficiency of the cryogenic solid propellants compared with conventional storable solid drives, hybrid drives or liquid driving gears, and to improve in a simple manner the storage properties and economic efficiency of said propellants, avoiding costly liquid management, and simultaneously eliminating the permanent ignition of the cryogenic solid propellants. To this end, the at least one liquid or gaseous phase embodied as a reactant in the form of a fuel or an oxidizer is transferred into a solid structure comprising interconnected cavities, said structure consisting of reactants which are formed in such a way that they complement the liquid phase, and the liquid phase is converted into a cryogenic solid phase inside the solid structure by means of freezing, said solid phase being stable below normal temperature.

The invention relates to a method of producing monergole solidpropellants [solid monopropellants] cooled below room temperature(cryogens] especially from heterogeneous liquid/solid propellants inwhich at least one of the reactants as oxidizer or fuel contains a phasewhich is liquid or gas at standard [normal] temperature, for example anemulsion of mutually insoluble liquid components, suspensions of solidsin liquid components or liquid/impregnated bulk material.

The invention relates further to a solid propellant cooled below roomtemperature [cryogenic solid propellant] for rocket drives, especially aheterogeneous quasimonergole [monopropellant] propellant-oxidizercombination in which at least one of the reactants is a liquid or gasphase at standard temperature, for example, an emulsion of liquidcomponents which are not mutually soluble, a suspension of a solidcomponent in a liquid component, or a liquid impregnated bulk material.

The invention is thus in the technological field of propellants forrocket drives and their fabrication and the development of solidpropellant combinations. As such, it should be understood that withinthe framework of the invention are specific geometric forms of simplepropellant blocks and assemblies thereof. This encompasses as wellpossible inclusions such as baffles and the like which can beincorporated in the block and which in uncooled propellants capable ofstorage are included for mechanical reasons as seals, combustioninhibitors, as melt loss inhibitors or for other reasons and in the caseof cryogenic solid propellants serve for or as support, filling,emptying or cooling devices. In both cases, during combustion or firing,in operation they may be completely or partly burned up.

With all known rocket fuels, the components are in a liquid and/or solidaggregation state and serve as oxidizers or as fuel. Many have stillother functions and can act for example as binders or additives.

Independently of the state of aggregation, propellant substances whetherhaving oxidizer or fuel functions can be considered as individual ormonergole substances (single component fuel substance). By separatingthe functions for different components, one can have diergoles.Monergoles can, dependent on their phase structure and their molecularcomposition a homogeneous or heterogeneous aggregation state. Examplesof homogenous monergoles as liquid propellants are hydrogen peroxide,hydrazine and nitroglycerin. Heterogeneous monergoles encompass forexample emulsions of liquid components which are not mutually soluble.

An entire series of preparations for rocket drives are known which haveat least one of the components in a liquid phase at standard temperature(U.S. Pat. No. 2,802,332, U.S. Pat. No. 3,367,268, U.S. Pat. No.3,398,215, U.S. Pat. No. 3,687,746, U.S. Pat. No. 3,697,455, U.S. Pat.No. 3,703,080).

U.S. Pat. No. 2,802,332 describes a propellant system for a liquidrocket which has a structure formed by a multiplicity of cells. Each ofthese cells contains at least one reactant. The walls of the cell-likestructure are comprised of polyethylene, Teflon or silicone rubber. Theindividual cells are connected with one another by openings.

The state of the art of U.S. Pat. No. 3,367,268 deals with a hybridrocket propellant system which is formed by a solid polymeric cell-likerubber substance which forms an intercellular matrix. In this matrixpulverulent fuel, for example, a light metal powder from groups II andIII of the periodic system of the elements and reinforcing fibers areembedded. The pores contain a liquid oxidizer.

In U.S. Pat. No. 3,398,215 a method of making a rocket propellant systemis described in which a hardenable rubber polymer is mixed withpulverulent metal fuel and a hardener and is treated as an organicpreparation. The rubber polymer is selected from the group ofrubber-like hydrocarbons and the halogenated hydrocarbon rubbers. As themetal fuel, powders of aluminum, boron, titanium, beryllium, magnesiumand lithium are used. The organic preparation boils at 70 to 200° C. andis compatible with the polymer. It is evaporated at the hardeningtemperature of 120° C. to 205° C. in the composite to form pores orcells therein. The foam-like matrix contains the metal fuel and forms aphase which holds together. The matrix is then immersed in an oxidizerliquid so that the pores are filled with the oxidizer liquid. All ofthese known solutions have the common drawback that they are able toachieve only a very low power level and are complicated in theirconstruction and handling.

It is also known to fabricate propellant systems in very differentgeometric forms. They can however be divided coarsely into twocategories, namely, internal burners with a plurality ofradially-directed burn-up segments and end burners with a plurality ofaxially directed burn-up segments.

Apart from monergole propellants [monopropellants] there are knownpropellants which contain the fuel and oxidizer as separate elements invarious geometric arrangements. Examples are radially burning diskstacks or rod-in-matrix end burners (R. E. LO, N. EISENRIECH; “Modulareund kryogene Feststofftreibsätze—eine neue Klasse chemischerRaketenantriebe”, Deutscher Luft—und Raumfahrtkongress, DGLR-JT98-104;Bremen, Jul. 10, 1998; Jahrbuch 1998, Band 2, S. 1231) (Modular andcryogenic solid propellant systems—a new class of chemical rocketdrives). Such arrangements are designated as modular drive systems.Modular drive systems with which modular elements are in the diergole[two component preparants] classification. The burn involves a diffusionframe with so-called boundary layer burns which is not followed or noteasily followed by a transition to an end controlled explosion ordestination. One should also distinguish encapsulated componentspropellants from modular propellants. The goal of encapsulation is themutual separation of reactive liquids and thereby the improvement in thelong-term storage capabilities. Liquids or very sensitive reactants canbe included in the capsules. No capsules are incorporated in anundirected manner in binders. Minor propellants are oriented and cast inplace with a binder or hardenable solid propellant. With increasingcapsule size (see R. M. McCURDY et al “Solid Propellant Grain ContainingMetal Macarocapsules of Fuel and Oxidizer”, U.S. Pat. No. 3,527,168) andan oriented arrangement, encapsulated propellants move into the subclassof rod-in-matrix preparations.

With smaller element dimensions and especially when the elements becomeno longer uniform but rather are statistically arranged, one obtainswith all known propellants a transition to the heterogeneous monergoleclass. The preparation combinations which are thus formed can best bedescribed as “quasimonergoles”.

The same relatively poor boundaries between monergoles and diergoles canbe found in the case of filled foam propellants and propellant bulkmaterials which are incorporated in a cast matrix. These two classes ofpropellant have in common modular propellant systems that they arehardly interesting for practical use in rocket drives because of thestorage characteristics although the reasons differ. In the case ofmodular solid propellants the choice of storable propellants is limitedbecause of energy availability grounds. Where there is a greaterselection in the case of liquid propellants, these are limited becauseof the solid phases used in solid/liquid heterogeneous bulk materialsand foam. The characteristic limitations derive from their limitedsuitability under propellant operating conditions where separation ofthe liquid phase must be avoided absolutely. While encapsulation is apossible solution, it is burdened by the complex fabrication conditions.When the capsules grow to the size of bars as in the case of modularrod-in-matrix propellant systems, the methods for composites of liquidsbecome no longer suitable.

Apart from the storable solid propellant systems, propellants which havebeen frozen have been proposed. These can have components which areliquids or gases at standard temperature. Such propellants are heredesignated as cryosolid propellants (cryogenic solid propellants orCSP).

Monergole CSP are comprised of frozen monergoles which are liquid atroom temperature. Modular CSPs are assembled from at least frozenelements which cannot be burned alone (U.S. Pat. No. 3,137,127). Theburning of modular nonmonomergole propellant elements are basically adiffuse boundary layer burn and as such, dependent upon the flow ofreactants. This flow is not effected as a force flow but only proceedsby convection, the reaction is not controllable and drags whenever itpredominates. As a result modular drive systems at least from a certainsize of the element, require one or more ignition discharge generators(U.S. Pat. No. 6,311,479).

In this state of the art the invention has as its object to increase thepower availability of cryosolid propellants by comparison withconventional solid propellants, hybrid propellants or liquidpropellants, to improve the storability and economy of a rocketpropellant while avoiding expensive liquid management and eliminatingsimultaneously the need for permanent ignition of cryosolid propellantsin a simple way.

This object is attained with the method of the type set out at theoutset with the characterizing method to prepare a solid propellant andthe solid propellant per se.

Advantageous refinements can be deduced from the dependent claims. Themethod according to the invention is characterized above all in that bythe freezing of the liquid phase in a heterogeneous liquid-solidpropellant, so that the latter can be converted to a cryogenic monergolesolid propellant whereby the permanent ignition can be dropped andproblems of liquid management which may arise with normal liquid-solidquasimonergoles can be overcome.

The invention covers therefore all quasimonergole fuel-oxidizercombinations in which at least one of the components is a frozen liquid.The invention yields a significant power increase for carrier rockets.Apart from the environmental compatibility of the drive, the inventionenables a choice of suitable propellant candidates like for example SOXor SH₂O₂ in combination with solid hydrocarbons like PE, PU, HTPB tosignificant operating and this starting cost saving pairings. In spiteof apparent but not relevant technological problems of cryogenic solidrockets, the invention enables for them a potentially greater market inrocket technology.

Further advantages and details are given in the following descriptionwith reference to the accompanying drawing.

The invention will be described in greater detail with a specificexample.

The drawing shows:

FIG. 1 a section through a polymer foam as a solid structure with acryogenic phase incorporated therein,

FIG. 2 a section through an aluminum foam as a solid structure with anincorporated cryogenic phase and

FIG. 3 a section through a cast packing of polyethylene and cryogenicphase.

The rocket drive system of a solid propellant according to the inventionshould be made by the method of the invention.

The solid propellant should, as FIG. 1 shows, be comprised of a polymerfoam 1, for example of polyethylene as a fuel and a cryogenic oxidizerphase 2, for example frozen hydrogen peroxide. The foam 1 as a solidphase is initially affixed to the internal insulation of a fuel chamberwall which has not been shown and then has its capillaries filled withhydrogen peroxide utilizing capillary forces or a pressure gradient andthen frozen in the foam 1 as required by undercooling. The hydrogenperoxide remains as a cryogenic phase in the foam 1.

Naturally it is also possible without departing from the invention tofoam the foam 1 directly in the combustion chamber.

The combustion of the solid propellant according to the invention isthen effected analogously to the classical solid fuel combustion in thecombustion chamber whereby the propellant is ignited by means of anigniter.

FIG. 2 shows an example in which an aluminum foam 3 is used as the solidphase and has its pores filled with frozen oxygen. The production of thesolid propellant according to the invention is effected as has beendescribed previously.

FIG. 3 shows a polyethylene packing 4 whose interior is filled with anoxidizer 5 which is liquid at room temperature and after filling hasbeen frozen.

The following table shows the range of applications of the presentinvention in which two components are provided in each case and wherebythe oxidizer formed by one component of the fuel formed by the othercomponent are each replaceable by others. Each component can then be ahomogeneous or heterogeneous mixture of different substances.

Note should be taken especially that naturally also high energymaterials, for example representatives of high energy density matter(HEDM) as components or additives can be considered, especiallydispersed atoms or molecules in a stabilizing matrix, stressed compounds(for example CUBAN), weakly covalent components (polynitrogencompounds), excited atoms or activated atoms or molecules (triplethelium) or metallic hydrogen. The cryogenic temperature provides astabilization of the HEDM and is absolutely relevant to its use.

The different possibilities of the topologies of the components are notconsidered here, that is in the following table, it is not criticalwhether foams or bulk material or packings are used or whether or notthese are mentioned as examples. Materials are described as “storable”when they have the given state of aggregation at room temperature and as“cryogens” when they require cooling as a rule on one of theabove-mentioned grounds.

It suffices to observe that in solid rocket propellant systems allcomponents will have the same starting point temperature regardless oftheir nature.

TABLE MORPHOLOGY OF CRYOGENIC QUASI-MONERGOLES COMPONENT 1 COMPONENT 2EXAMPLES Storable solid Cryogenic solid Plastic foam impregnated withfrozen hydrogen peroxide (SH₂O₂) or oxygen (SOX) with fuel particles ofplastic or metal embedded therein Storable solid Cryogenic liquidCapsules or tubes of cryogenic components in solid Cryogenic solidCryogenic solid Frozen oxygen with frozen fuel in any possiblequasi-monergole composition, for example SMOX (solid methane and solidoxygen) Cryogenic solid Storable liquid Frozen H₂O₂ with liquid fuelencapsulated therein Cryogenic solid Cryogenic liquid Combinations offrozen hydro- carbons with liquid oxygen encapsulated therein Cryogenicliquid Cryogenic or Bulk material (packing) of storable liquid capsulesof both components bonded together with an additional binder

The invention claimed is:
 1. A method of making a cryogenic solidmonergole propellant out of a heterogeneous liquid-solid propellant,from reactants at least one of which is a fuel and an oxidizer whichcontains a phase that is liquid or gaseous at standard temperature,which comprises the steps of: (a) incorporating at least one liquid orgaseous phase reactant in the form of an oxidizer in a solid phasestructure, open pore plastic foam fuel, having hollow spaces which areconnected to each other; and (b) transforming the liquid or gaseousphase oxidizer incorporated in the solid phase structure, open poreplastic foam fuel, having hollow spaces connected to each other byfreezing the liquid or gaseous phase into a stable cryogenic solid phasebelow standard temperature within the hollow spaces of the solid phasestructure, open pore plastic foam fuel, inside a combustion chamber toobtain a rocket propellant with improved storability while avoiding theneed for liquid management and simultaneously eliminating need forpermanent ignition thereof.
 2. The method of making a cryogenic solidmonergole propellant defined in claim 1 wherein the at least one liquidor gaseous phase reactant is an emulsion of liquid components which arenot soluble in one another.
 3. The method of making a cryogenic solidmonergole propellant defined in claim 1 wherein the at least one liquidor gaseous phase reactant is a suspension of solid components in liquidcomponents or liquid impregnated bulk materials or packings.
 4. Themethod of making a cryogenic solid monergole propellant defined in claim1 wherein the open pore plastic foam fuel is a polyethylene foam, apolyurethane foam, a HTBP foam, or a GAP foam.
 5. The method of making acryogenic solid monergole propellant defined in claim 1 wherein thesolid phase structure, open pore plastic foam fuel, having hollow spacesis a packing incorporated in a casting material and composed ofpolyethylene, polyurethane, HTPB, or GAP.
 6. The method of making acryogenic solid monergole propellant defined in claim 1 whereinaccording to step (a) the liquid phase is incorporated in the solidphase structure by immersion and/or impregnation thereof.
 7. The methodof making a cryogenic solid monergole propellant defined in claim 1wherein according to step (a) the liquid or gas phase reactant isoxygen, a hydrocarbon, hydrogen peroxide or an HEDM propellant.
 8. Themethod of making a cryogenic solid monergole propellant defined in claim1 wherein according to step (b) the solid monergole propellant isproduced by freezing liquid oxidizer.
 9. The method of making acryogenic solid monergole propellant defined in claim 8 wherein theliquid oxidizer is oxygen, a hydrocarbon, hydrogen peroxide or an HEDMpropellant.
 10. The method of making a cryogenic solid monergolepropellant defined in claim 1 wherein according to step (a) the liquidphase is initially encapsulated, then mixed with the solid phasestructure and bonded with the binder.
 11. The method of making acryogenic solid monergole propellant defined in claim 1 whereinaccording to steps (a) and (b) the liquid phase is encapsulated andbefore freezing the liquid phase, the solid phase structure is mixedtherewith, and both phases are frozen together.
 12. The method of makinga cryogenic solid monergole propellant defined in claim 1 whereinaccording to step (a) combustion speed of the cryogenic solidmonopropellant system is adjusted by selecting a special hollow spacesize in the solid phase structure.
 13. A stabilized cryogenic solidmonergole propellant for a rocket motor combustion chamber equipped withan inner isolation which comprises a solid or heterogeneousquasi-monergolic fuel oxidizer combination cooled to below ambienttemperature, wherein at least one reactant for preparing said propellantis an oxidizer in a liquid or gaseous phase at standard temperature, andat least one reactant for preparing said propellant is in a solid phasestructure, open pore plastic foam fuel, having hollow spaces which areconnected to each other, arranged at an inner isolation of thecombustion chamber or completely filling the latter, the solid phasestructure, open pore plastic foam fuel, having hollow spaces completelycontaining the liquid or gaseous oxidizer reactant cryogenicallytransformed and stabilized as a cryogenic solid.
 14. The stabilizedcryogenic solid monergole propellant defined in claim 13 wherein the atleast one reactant for preparing said monergole propellant in a liquidor gaseous phase at standard temperature is an emulsion of liquidcomponents not soluble in one another.
 15. The stabilized cryogenicsolid monergole propellant defined in claim 13 wherein the at least onereactant for preparing said propellant in a liquid or gaseous phase atstandard temperature is a suspension of solid components in liquidcomponents.
 16. The stabilized cryogenic solid monergole propellantdefined in claim 13 wherein the at least one reactant for preparing saidmonergole propellant in a liquid or gaseous phase at standardtemperature is a liquid impregnated packing.
 17. The stabilizedcryogenic solid monergole propellant defined in claim 13 wherein theopen pore plastic foam fuel is a polyethylene foam, a polyurethane foam,a HTBP foam, or a GAP foam.
 18. The stabilized cryogenic solid monergolepropellant defined in claim 13 wherein the solid phase cryogenicallytransformed from the liquid or gaseous phase is comprised of a stablesolid.
 19. The stabilized cryogenic solid monergole propellant definedin claim 18 wherein the solid phase cryogenically transformed from theliquid or gaseous phase as a stable solid is transformed oxygen,hydrocarbons, hydrogen peroxide, or an HEDM propellant.
 20. Thestabilized cryogenic solid monergole propellant defined in claim 13wherein the solid phase structure, open pore plastic foam fuel, havinghollow spaces is comprised of a packing of optionally shaped individualpieces whose hollow spaces are connected together in which a frozenliquid oxidizer is contained as a reactant.
 21. The stabilized cryogenicsolid monergole propellant defined in claim 20 wherein the frozen liquidreactant is not in homogeneous form but itself is a packing which ismixed into the hollow space of the first packing.
 22. The stabilizedcryogenic solid monergole propellant defined in claim 13 wherein thesolid phase structure, open pore plastic foam fuel, having hollow spacesis provided with a protective coating which chemically insulates thesolid phase structure, open pore plastic foam fuel, from the reactant inthe liquid or gaseous phase.